The aqueous emulsion polymerization and copolymerization of fluorinated, especially perfluorinated, monomers requires an emulsifier to stabilize the polymer particles in the liquid phase. Besides the ability to stabilize the particles and to prevent coagulation, the emulsifier should be inert under the polymerization conditions. In particular, emulsifiers that participate in chain transfer reactions should generally be avoided, as they tend to decrease the molecular weight of a polymer, whereas the desired molecular weight for fluoropolymers is usually quite high.
Accordingly, fluoropolymers have traditionally be polymerized in the presence of highly fluorinated or even perfluorinated emulsifiers, such as carboxylic and sulfonic acids and their salts, especially their ammonium salts.
While many materials may fulfil these requirements, industrial applications quickly converged upon the use of the ammonium salts of perfluorinated sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA).
Over the last 25 years, however, an increasing number of scientific papers have been published detailing findings of PFOS and PFOA widely spread in the environment and in the blood of the general population. This environmental persistence and bioaccumulation has come under regulatory scrutiny. The United States Environmental Protection Agency (US-EPA) has held a number of hearings since 2000 regarding this material.
In May of 2000, 3M, decided to cease production of PFOS and PFOA. The phase out of PFOA was a challenge for the fluoropolymer industry, as there were very few alternative emulsifiers readily available to replace PFOS and PFOA.
In 2006, the US-EPA invited eight companies—including fluoropolymer manufacturers—to participate in a voluntary program to reduce global emissions of PFOA by 95% by 2010 and to work toward the elimination of PFOA by 2015. Meanwhile, PFOS and perfluorinated carboxylic acids with 11 to 14 carbon chain length are listed in Europe under its Regulation, Evaluation and Authorization of Chemicals (REACH) program as substances of very high concern (SVHC). It was also recommended to list PFOA as an SVHC under REACH.